How to calculate needed lumens in a room?

kate1234March 4, 2007

What would the formula be to figure out how many total lumens you might want in a room? I realize there won't be one answer to a given sized room - that it will depend on

how bright one likes a room to be (bright but on a dimmer),

how good your eyesight (we're getting older),

how light the surfaces are (light oak floor, white painted cabinets, white tile backsplash, stainless appliances, white ceiling, light tan paint in just a few places, and dark shiny granite).

The kitchen is 10' x 12.5' with an 8' ceiling. I will have undercabinet lighting plus cans and I am just trying to figure out how many lumens those cans should have all together.

Thank you for reporting this comment. Undo
Jon1270

Hi Kate,

I saw your question addressed to me on Dinger's thread, too, but the weekend's been busy. The method I've used is something I came up with on my own, and I'm just an enthusiastic amateur; I'm sure a degreed lighting engineer would have a much more sophisticated approach. I think lumens are primarily useful for gauging ambient light, and that task lighting on countertops is better addressed with footcandle calculations. Anyhow, I think of ambient light as the light bouncing randomly around the room from one surface to another, illuminating the whole, general space rather than a particular surface. I estimated the surface area of the walls, floor and ceiling of my own little galley kitchen (450 square feet) and the nominal lumens generated by the half-dozen 50PAR20 bulbs that I've got in the ceiling (3300 total) and came up with a figure of 7.3 lumens per square foot (walls and ceiling included, remember; this is not just floor area) as a data point to describe my own kithen. Since I sometimes wish I had a bit more light in my kitchen, I figured it might be good to shoot for a bit more than 7.3 lm/sf, so I started using (in a purely intuitive, guesstimate sort of way) a figure of 8.5 lm/sf as a target when suggesting lighting arrangements for other people who asked.

This is a blunt and highly subjective instrument, meant only to avoid ending up with a room that resemebles a cave or an operating theater. As you said, surface reflectances, personal preference and the age of the viewer (I'm 36), not to mention other issues like fixture efficacy and available natural light, can play significant parts, and none of these are mathematically accounted for in this approach. But, then, to account for them mathematically would require a lot of data that isn't typically available in the context of these online chats about particular rooms in distant parts of the country or world.

So, your 10' by 12.5' by 8' kitchen has a walls/floor/ceiling surface area of around 610 square feet. My little 8.5 lm/sf target suggests you might want to build in the capacity to generate at least 5185 total lumens. A basic 50 watt PAR 30 lamp produces about 660 lumens, so I'd think in terms of using about 8 of them to light up that room. This would you give you more general light than I've got, and most of your surfaces are lighter than mine (I've got a lot of earth tones), so that's probably still a decent number despite the fact that you're "getting older."

March 5, 2007 at 7:41AM
Thank you for reporting this comment. Undo
carolina_2008

I been also looking for this question for my ceiling light and got some answers from one forum. Got a little bit encourage and they send me some hints on how.

This link might be useful: http://www.highend.com/support/training/lightingfaq.asp

February 22, 2008 at 10:25AM
Thank you for reporting this comment. Undo
kaseki

Lighting requirements depend on the type of work being performed (how finely one has to see and what the object's contrast is against its background) and the worker's age. I have seen tables for these factors on the www but cannot provide a reference. A search may prove illuminating.

kas

March 9, 2008 at 2:08PM
Thank you for reporting this comment. Undo
mikie_gw

fwiw
A quick web search puts ies minimum recommendations at 30FC for residental kitchens yet some califonia city that quoted that ies figure requires a minimum of 40 fc design. Which is smart because todays fluorescent lights, their advertised initial lumen output degrades over time, fairly quick on many of them.

another fwiw;
In general a quick way to roughly estimate lumen requirements, which amazingly works pretty well with normal light color ceil and walls, is foot candles will after losses be 50% of the total lamp rated lumens. If that makes any sense to ya.

Another words for general lighting at 40 fc;
10 x 12.5 room = 125 sq ft x 40 fc = 5000 total fc x 2 because lumens are only 50% efficient coming out of a fixture and bouncing around = 10,000 total lamp lumens required to get that 40 foot candles & should be pretty decent lighting.

However - I seriously doubt you actually need that many lumens because there really is no reason to light up every square foot of the kitchen area with light levels suitable for food preporation or to wash dishes. You're are going to want those levels concentrated on your counter top with task lighting. The work area's is what really counts, not the whole of the room.

March 10, 2008 at 10:03AM
Thank you for reporting this comment. Undo
john2_team

A random research about the same topic, and i found that there are many factors which affects while calculating lumens in a room. I was searching specifically for led lights. so it does make difference if lights are placed in center or are near to the wall on the ceiling. dark wall color will require more illumination.

i learnt this on a website where it explains how many led lights are sufficient for rooms. and for quick calculation you can head over to lumens calculator page: http://www.charlstonlights.com/led-light-requirement-calculator

Here is a link that might be useful: Lumens Calculator

This post was edited by john2_team on Mon, Jul 14, 14 at 7:11

July 14, 2014 at 6:38AM
More Discussions
Retrofitting off-sized recessed lighting with LEDs-Help?
We are renovating our just-purchased apartment and...
lindy74
MR16 vs GU10
What is the difference between MR16 and GU10 halogen...
mtvhike
dbruederlin
Rosette on slanted dining room ceiling?
Moved into a resale which has a dining room fixture...
Barb P
Need help finding black lantern sconces
I am trying to find black lantern lights like this....
marthasiny
'Dive into Sunshine Florida' Throw Pillow
\$29.99 | zulily
Caviar and Papyrus Polyester Filled 22 x 22 Pillow
\$48.00 | Bellacor
Lyle Celadon Blue Green Bubble Ceramic Table Lamp
\$69.99 | Lamps Plus
Home Decorators Area Rug: Omega Multi 8' x 11'
Home Depot
Montpellier Dual-tone Sectional Sofa Set with Matching Ottoman
Overstock.com
Venezia T-2535 Linear Suspension by Estiluz
\$1,842.00 | Lumens
Terminal Sofa
Dot & Bo
Inval White Wall Mount Hutch Bookcase
Overstock.com
People viewed this after searching for:
© 2015 Houzz Inc. Houzz® The new way to design your home™